Plasma coated sutures

ABSTRACT

Suture filaments coated by a plasma polymerization process exhibit a good balance of knot run down and knot security characteristics, superior tissue drag characteristics, and improved fray resistance.

BACKGROUND

1. Technical Field

The present disclosure relates generally to coatings for filaments. Moreparticularly, the present disclosure relates to silicone coatings forfilaments or sutures formed by a plasma polymerization process.

2. Background of Related Art

Many synthetic materials are presently used as surgical sutures. Thesematerials may be used as single filament strands, i.e., monofilamentsutures, or as multifilament strands in a braided, twisted or othermultifilament construction. Synthetic sutures have been made frommaterials such as polypropylene, nylon, polyamide, polyethylene,polyesters such as polyethylene terephthalate, and segmentedpolyether-ester block copolymers. In addition, absorbable syntheticsutures have been prepared from synthetic polymers such as polymerscontaining glycolide, lactide, dioxanone, caprolactone, and/ortrimethylene carbonate. Natural materials have also been used to makesutures. For example, silk has been used to make non-absorbable sutures.As another example, catgut sutures are absorbable sutures made from anatural material.

Sutures intended for the repair of body tissues must meet certainrequirements: they must be non-toxic, capable of being readilysterilized, they must have good tensile strength and have acceptableknot-tying and knot characteristics. The sutures should also besufficiently durable from the point of view of fray resistance.

The performance of a suture in terms of knot run down, knot security andtissue drag are particularly important to surgeons. Knot run downperformance, which reflects the ease of placement of a knot tied in asuture, is important in surgical procedures where it is necessary that aknot be tied in a suture when the knot is deep inside a surgical ornatural opening. For instance, a dental surgeon may need to tie a knotinside a patient's mouth. An intravaginal hysterectomy requires suturingin restricted quarters. One technique frequently used is to tie a squareknot that can be run down from an exterior location where the knot isfirst tied to lie against tissue with a desired degree of tightness. Theknot is snugged down so that it is holding with a degree of firmnesschosen by the surgeon for a particular situation and then additionalthrows, utilized to form additional knots, are tied down against thefirst throws of the square knot. In some instances, the first throw is adouble twist followed by a single throw to form a surgeons' knot, withadditional throws to form additional square knots on top as needed. Theease with which a knot runs down the suture depends on a number offactors such as composition of the suture, braid structure of thesuture, and the nature of the coating, if any, applied to the suture.Preferably, the knot runs down the suture smoothly and easily.

Knot security is the ability of the knot to hold without slipping for anacceptable length of time. The characteristics of the suture materialwhich allow a knot to hold securely are somewhat at odds with thecharacteristics of the suture material which provide satisfactory knotrun down performance, since knot security requires that the suture grabitself while knot run down requires that the suture pass smoothly overitself. Accordingly, a balance of these two characteristics is normallyrequired.

Some synthetic sutures, especially polypropylene monofilament sutures,have a tendency to fray as the suture passes over itself, e.g., whentying knots. While the limited amount of fraying exhibited by thesesutures does not substantially hamper the performance of the suture,there remains room for improvement in the processing and thecharacteristics of such sutures.

It is also desirable for a suture to have low tissue drag, which is ameasure of the force required to pull a suture through tissue. High dragforces result in chatter as the suture passes through tissue, make itmore difficult for the surgeon to align tissue neatly, and increase thetime to complete the closure being made with the suture.

A wide variety of coatings have been applied to sutures of various typesto improve one or more characteristics of the suture. See, for example,U.S. Pat. Nos. 3,187,752; 3,527,650; 3,942,523; 4,105,304; and4,185,637. These coatings include silicones. See U.S. Pat. No.3,187,752.

Fibers or textile treatments which include organo silicon compounds havebeen described in, inter alia, U.S. Pat. Nos. 3,280,160; 3,418,354;4,283,519; 4,359,545; 4,217,228; 4,784,665; 3,837,891; 4,207,071;4,184,004; 4,578,116; 4,937,277; 4,617,340; and 4,624,676.

Siloxane-oxyalkylene copolymers have been described in U.S. Pat. Nos.3,629,310; 3,755,399; 3,280,160; 3,541,127; and 4,699,967. U.S. Pat. No.5,383,903 discloses coating a surgical suture with adimethylsiloxane-alkylene oxide copolymer lubricant.

The above coatings are applied by means known to those skilled in theart, e.g., dipping, spraying, etc.

It would be advantageous to apply coatings possessing improvedmechanical strength to sutures in order to further enhance the sutures'handling characteristics.

SUMMARY

It has now been found that a suture coated by a plasma polymerizationprocess whereby a siloxane monomer is polymerized onto the suturesurface exhibits a good balance of knot run down and knot securitycharacteristics, superior tissue drag characteristics, and improved frayresistance.

In another aspect, the present disclosure embraces a method forimproving the handling characteristics of a suture by utilizing a plasmapolymerization process to apply to the suture a coating comprising asiloxane polymer.

Preferred coatings are formed by a plasma polymerization process wherebyaliphatic hydrocyclosiloxane monomers are polymerized on the surface ofthe suture to form a siloxane coating on the suture. In one embodiment,amine groups are introduced onto the polymer coating by co-polymerizingan organo-based monomer with the aliphatic hydrocyclosiloxane monomer orby carrying out a second plasma polymerization process for theintroduction of the organo-based monomer. The amine groups on thepolymer coating may then be reacted with carbonate polyoxyalkylenes togive polyoxyalkylene modified polymer coatings which enhance thehandling characteristics of the coated sutures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Sutures treated in accordance with the present disclosure can befabricated from a wide variety of natural and synthetic fibrousmaterials. Such materials include non-absorbable as well as partiallyand fully bioabsorbable (i.e., resorbable) natural and syntheticfiber-forming polymers. Non-absorbable materials which are suitable forfabricating sutures include silk, polyamides, polyesters such aspolyethylene, polypropylene, cotton, linen, etc. Carbon fibers, steelfibers and other biologically acceptable inorganic fibrous materials canalso be employed. Bio-absorbable sutures may be fabricated from naturalcollagenous material or synthetic resins including those derived fromglycolic acid, glycolide, lactic acid, lactide, dioxanone, caprolactone,polycaprolactone, epsilon-caprolactone, trimethylene carbonate, etc.,and various combinations of these and related monomers. Sutures preparedfrom resins of this type are known in the art. See, e.g., U.S. Pat. Nos.3,297,033; 3,839,297; and 4,429,080.

Preferably, the suture is made from a synthetic material. Suitablesynthetic materials include, but are not limited to, polypropylene,nylon, polyamide, polyethylene, polyesters such as polyethyleneterephthalate, segmented polyether-ester block copolymers andpolyurethanes.

Sutures treated in accordance with the present disclosure can have oneor more filaments. When more than one filament is used, the filamentsmay be braided, twisted, entangled, intertwined or arranged in someother multifilament configuration. A particularly useful braid structurefor sutures is the spiroid braid structure described in U.S. Pat. Nos.5,019,093 and 5,059,213 the disclosures of which are incorporated hereinby reference.

In a preferred embodiment, the sutures to be coated in accordance withthe present disclosure are made of synthetic polymers.

In general, sutures treated in accordance with the present disclosureare subjected to a plasma polymerization process to form a polymercoating on at least a portion of the surface of at least one filament ofthe suture. The term “plasma” refers to a thermodynamicallynon-equilibrium gaseous complex, composed of electrons, ions, gas atoms,free radicals, and molecules in an excited state, known as the plasmastate.

Plasma may be generated in a process known as plasma discharge by anumber of methods including combustion, flames, electric discharges,controlled nuclear reactions and shocks. The most obvious and commonlyused is electric discharge. Radio frequency (“RF”) or microwavedischarge are mainly used for polymerization reactions. For commercialRF generators, the frequency used in the process is dictated by theFederal Communications Commission and is set at 13.56 MHz.

Two opposing processes occur simultaneously during plasma discharge. Ingeneral, it can be said that the generation of free radicals in thevapor phase leads to the formation of thin films. However, at high powerof field strength, ions are generally responsible for ablation or“etching” of the surface of any article introduced into the plasma. Atvery low gas or monomer flow rates, there is little polymer depositionand the deposition rate decreases with increasing discharge power. Athigher flow rates, the deposition of polymer increases (linearly), butreaches a maximum with increasing discharge power and then ablationbecomes more predominant.

There are two types of commercially available plasma-statepolymerization systems: (a) capacitively coupled internal parallelelectrodes, such as Bell Jar reactors, and (b) RF coil-inductivelycoupled tubular reactors. Generally, without modification, these systemsare not suitable for producing the uniform single-phase coatings at highenough deposition rates and are more suitable for controlled etching ofan article's surface.

The most serious shortcoming of the above-mentioned commercial systemsfor polymer formation is their inability to control the monomer flow tothe region between the electrodes. This inability renders it impossibleto achieve uniform plasma density, plasma composition, or depositionrate between the electrodes. Furthermore, because the monomer is notconfined to the electrode region in these systems, the flow rate betweenthe electrodes is significantly decreased. In addition, because of theundirected monomer flow, oily and powdery deposits of plasma polymerizedmonomers form throughout the plasma chamber. One way to eliminate thesedeposits is by restricting the flow path in the reactor chamber to thespace between the electrodes, which maintains polymer deposition solelyin the plasma glow zone. Thus, when the plasma glow zone is activated,the monomer or monomer mixture is continually passed through the plasmaglow zone and the unused monomer or monomer mixture condenses in thecold trap.

In order to adequately form polymers on the suture surface, one mustunderstand the limitations of the commercially available systems notedabove and the parameters which affect the formation of a plasma coatingor membrane. The relationship between the plasma intensity, free radicalconcentration, and system pressure is complex. The plasma coatingparameter formula, W/FM, where W is the RF power, F is the monomer flowrate, and M is molecular weight of the monomer (see Yasuda, H., PlasmaPolymerization, Academic Press, 1985) fails to address two importantfactors: system pressure and the plasma reactor geometry.

At a given W and F, if the system pressure increases above a givenpressure, the resulting coating is no longer homogenous and a two-phasemorphology coating will start to appear. This two-phase phenomenon iscaused by an increase in the system pressure which decreases the meanfree path of monomer free radicals and results in the monomer freeradicals recombining in the gas phase before reaching the suturesurface. This in turn results in deposition of plasma polymerizedsiloxane powder along with polymerization of free radicals on the suturesurface, resulting in the two-phase coating. The W/FM parameters alsowill change when the geometry of the plasma reactor changes. Therefore,W/FM can be a useful plasma coating parameter only if the system ismaintained at constant pressure and only if the same plasma reactorgeometry is utilized.

A plasma coating system with the same reactor geometry can be used ifthe W/FM formula is employed as a control indicator. If the system iscontrolled at a given pressure, increasing W and decreasing F willlikely result in etching or ablation of the suture surface. If W isdecreased and F is increased, the desired coating will most likelyresult.

Modifications of the monomer flow rate and flow path are criticalfactors in avoiding two-phase coatings and obtaining the necessary highdeposition rates of plasma polymerized coatings on suture surfaces. Ingeneral, a high flow rate (about 5 μmole/sec), moderate R.F. power(about 80 W), and low system pressure (about 40 mTorr) will produce asuitable homogeneous siloxane coating.

The monomers used to form the polymer coating are polymerized directlyon the suture surface using plasma-state polymerization techniquesgenerally known to those skilled in the art. See Yasuda, PlasmaPolymerization, Academic Press Inc., New York (1985), incorporatedherein by reference.

In brief, the monomers are polymerized onto the suture surface byactivating the monomer in a plasma state. The plasma state generateshighly reactive species, which form the characteristically highlycross-linked and highly-branched, ultra-thin polymer coating, which isdeposited on the suture surface as it moves through the area of thereactor having the most intense energy density, known as the plasma glowzone.

For plasma polymerization to produce a coating on a suture, which mayalso be called “plasma grafting”, a suitable organic monomer or amixture of monomers having polymerizable unsaturated groups isintroduced into the plasma glow zone of the reactor where it isfragmented and/or activated forming further excited species in additionto the complex mixture of the activated plasma gases. The excitedspecies and fragments of the monomer recombine upon contact with thesuture surface to form a largely undefined structure which contains acomplex variety of different groups and chemical bonds and forms ahighly crosslinked polymer coating on the suture surface. If O₂, N₂, oroxygen or nitrogen containing molecules are present, either within theplasma reactor during the polymer coating process, or on exposure of thepolymer coated suture to oxygen or air subsequent to the plasma process,the polymeric deposit will include a variety of polar groups.

The amount and relative position of polymer deposition on the sutures isinfluenced by at least three geometric factors: (1) location of theelectrodes and distribution of charge; (2) monomer flow; and (3) sutureposition within the reactor relative to the glow region. In the case ofsuture fibers which are pulled continuously through the plasma chamber,the influence of the suture position is averaged over the length of thefibers.

In practice, an electric discharge from an RF generator is applied tothe “hot” electrodes of a plasma reactor. The selected monomers areintroduced into the reactor and energized into a plasma, saturating theplasma glow zone with an abundance of energetic free radicals and lesseramounts of ions and free electrons produced by the monomers. As thesuture passes through or remains in the plasma glow zone, the surface ofthe suture is continually bombarded with free radicals, resulting in theformation of the polymer coating.

In one embodiment, the plasma chamber used for plasma polymerization hascapacitively coupled plate-type electrodes. The sutures are exposed tomonomers having a mass flow rate in the range from about 50 to about 100standard cubic centimeters per minute (sccm), at an absolute pressure inthe range from about 40 mTorr to about 70 mTorr. The exposure timeranges from about 45 seconds to about 9 minutes. The currently preferredexposure time is in the range from about 2 minutes to about 6 minutes. Aradio frequency of 13.56 MHz in the range from about 25 watts to about100 watts generates sufficient energy to activate the monomers.

It will be appreciated by those skilled in the art that in a differentlyconfigured plasma chamber, the monomer flow rate, power, chamberpressure, and exposure time may be outside the ranges of that set forthfor the embodiment discussed above.

During the plasma polymerization process, the suture is subjected toboth thermal and ultra-violet (UV) radiation. The heat generated can beremoved by external fans constantly blowing onto the system. The heatgenerated by electrons, ions, or free radicals colliding with the suturesurface is insignificant and will not effect the bulk mechanicalproperties of the suture. While the total energy released as heat ormechanical energy after impact is relatively small, the surface of thesuture may become chemically active and unstable.

The UV radiation generated from the plasma process can be harmful topolymeric sutures, such as polypropylene fibers. The UV radiationpenetrates the surface of the suture, breaking the polymer chains at thesurface. This is known as chain scission. The polymer chains maysubsequently recombine. If polymer chain scission is the dominantprocess, the suture's mechanical strength will be weakened. If polymerchain recombination is the dominant process, the polymer units will formlocal cross-linked network structures, and the suture will loseductility and become brittle. Accordingly, the intensity of the plasmaglow zone, the substrate residence time in the plasma glow zone, and thesubstrate pulling tension need to be carefully controlled in order toachieve a proper balance between scission and recombination and minimizethe plasma-induced damage to the suture.

Where the proper balance between scission and recombination is achieved,the plasma polymerization process not only forms a thin layer ofpolymerized siloxane on the surface of the suture but, as noted above,the thermal and UV radiation generated by the plasma process alsoactivates the surface of the suture itself, permitting crosslinking ofthe siloxane coating with the polymeric suture material. Thecrosslinking of the siloxane coating with the suture surface increasesthe mechanical strength of the suture material, which enhances the frayresistance of the suture without substantially changing its bulkproperties.

In accordance with the present disclosure, siloxane monomers are used inthe plasma polymerization process to produce polymer coatings on thesuture surfaces. One preferred polymer coating which can be deposited onthe suture surface through the plasma state polymerization process ofthe present disclosure uses aliphatic hydrocyclosiloxane monomers of thegeneral formula:

where R is an aliphatic group and n is an integer from 2 to about 10,preferably 4 to 6.

Preferred aliphatic hydrocyclosiloxane monomers include:1,3,5,7-tetramethylcyclotetrasiloxane (“TMCTS”);1,3,5,7,9-pentamethylhydrocyclopentasiloxane (“PMCTS”);1,3,5,7,9,11-hexamethylhydrocyclohexasiloxane (“HMCHS”) and a mixture of1,3,5,7,9-pentamethylcyclopentasiloxane and1,3,5,6,9,11-hexamethylcyclohexasiloxane monomers (“XMCXS”). Use of aradio frequency power greater than 5 W, a system pressure less than 300mTorrs, and a monomer flow rate greater than 1 μmole/sec, will cause ahomogeneous, hard, hydrophobic, biocompatible, polymer coating with alow friction coefficient to form on the suture surface passing throughthe plasma glow zone.

The aliphatic hydrocyclosiloxane monomers noted above may be used tocreate a homogeneous coating on the suture surface. In anotherembodiment, the aliphatic hydrocyclosiloxane monomers may be mixed withco-monomers to give polymer coatings having properties different fromthe properties of the homogenous coating. For example, by introducingreactive functionalizing monomers, or organo-based monomers, orfluorocarbon monomers together with the aliphatic hydrocyclosiloxanemonomers in the plasma polymerization system, physical pore size andchemical affinity of the plasma copolymerized aliphatichydrocyclosiloxane coating with selective monomers can be controlled.This allows the use of the copolymerized plasma polymer coating forapplications which require the coating to differentiate between certaintypes of gases, ions, and molecules and it also may be utilized tointroduce functional groups to the polymer coating which, in turn, canimpart enhanced handling characteristics to the suture and also helplink other compounds or compositions to the polymer coating.

In a preferred embodiment, the polymer coatings may be produced by aplasma co-polymerization process of mixtures of the same aliphatichydrocyclosiloxane monomers noted above with organo-based monomers thatintroduce amine groups onto the polymer coating and form amine graftedpolymer coatings. It is more preferred to introduce these organo-basedmonomers onto the polymer coating in a second plasma grafting processwhich occurs after the plasma polymerization of the aliphatichydrocyclosiloxane monomers. Suitable organo-based monomers includeallylamine, N-trimethylsilylallylamine, unsaturated amines (bothN-protected and N-unprotected), and cyclic aliphatic amines (bothN-protected and N-unprotected). As used herein, the term “amine graftedpolymer coatings” refers to a polymer coating containing amine groups,which can be obtained either by co-polymerization of the organo-basedmonomer with the hydrocyclosiloxane monomer or by plasma grafting theorgano-based monomer onto a previously formed siloxane polymer coating.

In yet another embodiment, these plasma treated sutures, possessingamine grafted polymer coatings, are then reacted with carbonate-basedpolyoxyalkylene compounds to produce polyoxyalkylene modified polymercoatings. In a preferred embodiment, the carbonate-based polyalkyleneoxide is of the general formula

wherein R₁ is an N-benzotriazole group, an N-2-pyrrolidinone group, or a2-oxypyrimidine group; R₂, R₃ and R₄ are independently selected alkylenegroups of about 2 to about 3 carbon atoms and may be the same ordifferent; R₅ is selected from hydrogen, methyl, acarbonyloxy-N-benzotriazole group, a carbonyloxy-N-2-pyrrolidinonegroup, and a carbonyl-2-oxypyrimidine group; a is an integer from 1 to1000 and each of b and c is an integer from 0 to 1000, where a+b+c is aninteger from 3 to 1000. Suitable lower alkylene groups include thosehaving about 2 to about 3 carbon atoms.

In preferred compounds of the above formula, R₂, R₃ and R₄ is —(CH₂CH₂)—or —CH₂CH(CH₃)— or any combination thereof. More preferably R₂, R₃ andR₄ are ethylene. According to a preferred aspect a, b, and c areselected so as to give a molecular weight for the PEG moiety of about500 to about 20,000, more preferably from 3000 to 4000. Preferredpolyoxyalkylene carbonates include, but are not limited to,polyoxyethylene bis-(2-hydroxypyrimidyl) carbonate, polyoxyethylenebis-(N-hydroxybenzotriazolyl) carbonate and polyoxyethylenebis-(N-hydroxy-2-pyrrolidinonyl) carbonate.

These polyoxyalkylene modified polymer coatings impart a good balance ofknot run down and knot security characteristics, superior tissue dragcharacteristics, and improved fray resistance to sutures. In addition,these polyoxyalkylene modified polymer coatings possess apolyoxyalkylene tether capable attaching additional compounds, includinglubricants or bioactive compounds, to the polymer coating.

The resulting coating on the suture is between about 0.01 to about 10percent by weight based upon the weight of the filament or filaments towhich the coating is applied. Preferably, the coating is applied in anamount of from about 0.05 to about 7.5 weight percent. Most preferably,the amount of coating is between about 0.1 and about 5 weight percent.The amount of coating applied to the suture may be adequate to coat allsurfaces of the suture. Preferably, the amount of coating applied willbe that amount sufficient to improve the handling characteristics of thesuture, regardless of whether the entire surface of the suture iscoated. The term coating as used herein is intended to embrace both fulland partial coatings.

The amount of coating composition may be varied depending on theconstruction of the sutures, e.g., the number of filaments and tightnessof braid or twist. In a preferred embodiment, the depth of crosslinkingof the silicone coating with the surface of the suture is less thanabout 100 Å. The coatings may optionally contain other materialsincluding colorants, such as pigments or dyes, fillers or therapeuticagents, such as antibiotics, growth factors, antimicrobials,wound-healing agents, etc. Depending on the amount of coating present,these optional ingredients may constitute up to about 25 percent byweight of the coating.

An important feature of the present invention is the creation of acontinuous thin coating. The thickness of this coating can be determinedgravimetrically, and the continuity of the coating can be determined byits permeability. These factors, along with the chemical composition ofthe coating (i.e., carbon, silicone, oxygen, nitrogen percentages),determined by ESCA (electron spectroscopy for chemical analysis) aresome of the values which change as plasma parameters are modified.

The following examples should be considered as illustrative and not aslimitations of the present description. The examples show illustrativeformulations and the superiority of the present coating composition inenhancing properties of sutures.

EXAMPLE 1

This experiment analyzed the fray resistance of synthetic sutures madeof polypropylene (from United States Surgical, Norwalk, Conn.) treatedin accordance with the present disclosure. Care was taken to minimizehandling of the sutures, and whenever possible the sutures were handledwith plastic forceps.

The siloxane derivative, 1,3,5,7-tetramethylcyclo-terasiloxane (TMCTS,Hydrosilox®) was polymerized on the suture surface in a glow dischargeplasma deposition lasting for varying amounts of time, forming asiloxane-coated suture. The TMCTS plasma was generated at 83 W, 55mTorr, and a flow rate of 84 sccm. It was found that the application ofthe plasma coating for time periods ranging from 2 to 6 minutes formedpolymer coatings that prevented the fraying of the polypropylene suturematerial.

In some cases, a second plasma polymerization process, or plasmagrafting process, was utilized to introduce amine groups onto thepolymer coating. N-trimethylsilylallylamine (TMSAA) was plasma graftedto the siloxane-coated suture for 4 minutes at 65 mTorr, 35 W, and aflow rate of 42 sccm. This process introduced a protected amine to thesiloxane coating, that was subsequently modified in the next step.

Polyethylene oxide compound (PEOC) was used to prepare anactivated-intermediate HPEOC, a bifunctional-crosslinker polyoxyethylenebis-(N-hydroxybenzotriazolyl) carbonate. HPEOC was then conjugated tothe surface-bound primary amines during a 10 minute immersion in asolvent. During the conjugation, hydroxybenzotriazolyl carbonate wasliberated and polyoxyethylene-(N-hydroxybenzotriazolyl) attached to theamine via a urethane bond.

Sutures treated pursuant to this plasma polymerization process weresubjected to a test to determine their fray resistance. There were 3sets of sutures: 1-6 possessed a thin siloxane coating; 7-12 possessed athick siloxane coating; and 13-18 possessed a thick coating of HPEOCover siloxane. The fray test passes the suture repeatedly over itselfuntil the suture frays and eventually breaks (i.e., suture failure). Theresults, which are reported as number of cycles to suture failure, arepresented below in Table 1. TABLE 1 SUTURE DESCRIPTION #CYCLES TOFAILURE 1 Siloxane coating, thin 66 2 Siloxane coating, thin 61 3Siloxane coating, thin 68 4 Siloxane coating, thin 56 5 Siloxanecoating, thin 48 6 Siloxane coating, thin 63 7 Siloxane coating, thick28 8 Siloxane coating, thick 25 9 Siloxane coating, thick 47 10 Siloxanecoating, thick 194 11 Siloxane coating, thick 32 12 Siloxane coating,thick 23 13 Thick PEOC over siloxane 952 14 Thick PEOC over siloxane1500 (Stopped) 15 Thick PEOC over siloxane 1388 16 Thick PEOC oversiloxane 759 17 Thick PEOC over siloxane 4299 18 Thick PEOC oversiloxane 2268

EXAMPLE 2

This experiment compared a commercially available suture, Prolene MDE643(Ethicon, Inc.) with a Surgipro suture (United States Surgical)possessing an HPEOC conjugated siloxane coating that was prepared inaccordance with Example 1 above. The knot security, determined bywhether or not the knots broke or slipped, was determined for 6 of eachof the above sutures and the results are presented below in Table 2.TABLE 2 SUTURE BREAKING SLIPPING Prolene MDE643 6/6 knots broke 0/6slipped Surgipro with HPEOC 6/6 knots broke 0/6 slipped

The foregoing data show that sutures coated in accordance with thisdisclosure have knot security equivalent to commercially availablesutures, and thus exhibit an advantageous balance combination of goodfray resistance and knot security.

It will be understood that various modifications may be made to theembodiments disclosed herein. Therefore, the above description shouldnot be construed as limiting, but merely as exemplifications within thescope and spirit of the claims appended hereto.

1. A suture comprising: at least one filament; and a coating formed onat least a portion of a surface of the at least one filament by a plasmapolymerization process wherein a polymer coating is formed on thefilament surface from a hydrocyclosiloxane monomer of the generalformula

where R is an aliphatic group and n is an integer from about 2 to about10.
 2. A suture according to claim 1, wherein the hydrocyclosiloxanemonomer is selected from the group consisting of1,3,5,7-tetramethylcyclotetrasiloxane,1,3,5,7,9-pentamethylhydrocyclopentasiloxane,1,3,5,7,9,11-hexamethylhydrocyclohexasiloxane, and a mixture of1,3,5,7,9-pentamethylcyclopentasiloxane and1,3,5,6,9,11-hexamethylcyclohexasiloxane monomers.
 3. A suture accordingto claim 1, wherein the at least one filament is made from a synthetic,absorbable polymer composition.
 4. A suture according to claim 3,wherein the synthetic, absorbable polymer composition comprises ahomopolymer or copolymer derived from one or more monomers selected fromthe group consisting of glycolic acid, glycolide, lactic acid, lactide,dioxanone, caprolactone, polycaprolactone, epsilon-caprolactone,trimethylene carbonate, and combinations thereof.
 5. A suture accordingto claim 1, wherein the at least one filament is made from a synthetic,non-absorbable polymer composition.
 6. A suture according to claim 5,wherein the synthetic, non-absorbable polymer composition comprises oneor more materials selected from the group consisting of nylon andpolypropylene.
 7. The suture of claim 1, wherein the coating furthercomprises an amine group that has been introduced onto the coating byplasma polymerization of a gas containing a monomer selected from thegroup consisting essentially of unsaturated N-protected amines,unsaturated N-unprotected amines, N-protected cyclic aliphatic amines,and N-unprotected cyclic aliphatic amines, to produce an amine graftedpolymer coating.
 8. The suture of claim 7, wherein the unsaturated orcyclic amine is copolymerized with the hydrocyclosiloxane monomer ontothe surface of the at least one filament of the suture.
 9. The suture ofclaim 7, wherein the unsaturated or cyclic amine is plasma grafted ontothe coating on the surface of the at least one filament of the suture.10. The suture of claim 7, wherein said unsaturated or cyclic amine isN-trimethylsilylallylamine.
 11. The suture of claim 7, wherein acarbonate-based polyalkylene oxide compound is contacted with the aminegrafted polymer coating to produce a polyoxyalkylene modified polymercoating, the carbonate-based polyalkylene oxide compound comprising thegeneral formula

wherein R₁ is selected from the group consisting of N-benzotriazolegroups, N-2-pyrrolidinone groups, and 2-oxypyrimidine groups, R₂, R₃ andR₄ are independently selected from the group consisting of alkylenegroups having from about 2 to about 3 carbon atoms which may be the sameor different, R₅ is selected from the group consisting of hydrogen,methyl, carbonyloxy-N-benzotriazole groups,carbonyloxy-N-2-pyrrolidinone groups, and carbonyl-2-oxypyrimidinegroups, a is an integer from 1 to 1000 and each of b and c is an integerfrom 0 to 1000, where a+b+c is an integer from 3 to
 1000. 12. The sutureof claim 11 wherein said carbonate-based polyalkylene oxide compound ispolyoxyethylene bis-(N-hydroxybenzotriazolyl) carbonate.